Traditionally, plasma etch processes have been controlled by rigorous attention to parameters such as RF power, gas mixture composition and flow, chamber pressure, substrate temperature and load size. Unfortunately, the interaction of these parameters with respect to the plasma chemistry is complex, making process control difficult. Optical Emission Spectroscopy (OES) techniques offer an opportunity to monitor plasma chemistry directly and in real time. By viewing the discharge through a window in the chamber, this non-invasive technique can be applied to the many types of etching systems currently employed without any perturbation of the etch process. A fiber optic cable transports the optical signal from the window in the chamber to optical spectrometer for analysis.